Ribbon seal and method of fabrication



March 3, 19 T. c. RETZER ET AL 2,

RIBBON SEAL. AND METHOD OF FABRICATION FiledSept. 1, 1955 14 .30 25 IJZINVENTOM 44 48 Z4 44 7? c. Ear-2E2 Z4 44 flUUE/VEX 7 2,876,377 PatentedMar. 3, 1959 RIBBON SEAL AND METHOD OF FABRICATION Theodore C. Retzer,Cedar Grove, and Robert A. Gingras,

Preakuess, N. J., assignors to Westinghouse Electric 1 Corporation, EastPittsburgh, Pa., a corporation of Pennsylvania Application September 1,1955, Serial No. 531,883 6 Claims. Cl. 313-184 This invention relates toseals and, more particularly to ribbon-type seals for .high pressuregaseous discharge lamps, such as a quartz short are mercury lamp, and to.the method of protecting and maintaining the ribbon conductor in adesired preselected position within the stem portion of the lampenvelope during the sealing operation.

Seals capable of withstanding the high operating currents, temperatures,and pressures of mercury or xenon discharge lamps are generallyfabricated by embedding an extremely thin leading-in ribbon conductor ofrefractory material, such as molybdenum, in a tubular quartz arm or stemtube which forms part of the lamp envelope. In order to'facilitateelectrical connection with the electrode and-an external power supplyconnector strips of substantially greater thickness are usually attachedto eachend'of the main ribbon conductor thereby forming'a ribbonleading-in conductor assembly.

Heretofore, the ribbon assembly was either inserted into the tubularstem portion of the lamp envelope or, if extremely high current carryingcapacity was required, a plurality of ribbon assemblies were affixed tothe outer surface of a quartz 'retaining body which was, then insertedinto the stem tube. In either type of seal, after the ribbon assemblywas inserted into the stem tube the end of the "tube was sealed topermit evacuation of the envelope whereupon the stem tube was rotated ina high temperature fire until the quartz became plastic and was drawninto intimate contact with the ribbon conductor assembly to form ahermetic seal. Moreover, in order to effect a more perfect bond betweenthe quartz and the metal ribbon conductor it has been found'advantageousto gradually reduce the thickness of the ribbon extremities by achemical etching process to form an extremely thin edge, or, as it iscommonly referred to in the art, a feather edge. Due to the complexityof the type of seal required for high currents its use in the lowerWattage lamps is not practical from an economic standpoint. Hence, whererelatively low current carrying capacity is required, as in the case ofshort are lamps of under 500 watts capacity, the ribbon conductorassembly is generally sealed directly into the tubular stem portion ofthe lamp envelope. It has been found, however, that when the main ribbonconductor, particularly one that has a feather edge, has been sealed inthe stem tube in this manner the ribbon tends to become deformed or theedges become damaged when the stem tube is rotated during the sealingoperation by virtue of the fact that the inner walls of the tube areconsiderably closer to the edges of the ribbon than to the flat surfacesthereof. This type of sealing assembly and method of fabrication hasresulted in a large percentage of seals that leak, thereby causing highshrinkage in production or deleteriously affecting the useful life ofthe'lamp.

It is the principal objectof the invention, therefore, to avoid andovercome the foregoing and other difiiculties and objections to theprior art by providing a seal for 2 short are gaseous discharge lamps inwhich the' thin ribbon conductor is not deleteriously deformed or thefeather edgesv thereof damaged as a result of the operations required tomake the seal.

A further object is to provide a ribbon leading-in conductor andelectrode supporting assembly which will permit the electrode and ribbonconductors to be properly positioned within the lamp envelopeand;maintained in such position until the sealing operation has beencompleted.

Another object of the invention is to reduce'manufacturing costs andimprove the performance of short are gaseous discharge lamps byproviding a simple economic means of fabricating uniform ribbon-typeseals of high quality. I

A still further object is to provide a method of fabricating and sealinga leading-in conductor and electrode supporting assembly within the stemportionof a short are gaseous discharge lamp without deforming theribbon conductor or damaging the feather edge thereof.

The aforesaid objects of theinvention, and .other objects which willbecome apparent to those skilled: in the art asthe description proceeds,are achieved by enclosing the main ribbon conductor and a portion of theelectrode in quartz members to form a laminous .core of substantiallycylindrical configuration having such dimensions that'it makes a snugfit with the 'stemtube portion of thelamp envelope into which it is tobe sealed. Specifically, the main ribbon conductor and electrodesupporting assembly is so constructed that the. ribbon portion thereofmay be interposed between the two halves of a bisected quartz rod'whichhalves are held in the proper position for insertion into the stem tubeand are of substantially greater diameter than the width of the ribbonconductor so that the ribbon is totally enclosed and protected duringthe sealing operation.

For a better understanding of the invention reference should be had tothe accompanying drawings, in which like numerals of reference indicatesimilar parts through out the several views, wherein:

Fig. 1 is a front elevational view of a quartz. short are gaseousdischarge lamp employing the seal of this invention and showing theenvelope and two stem portions with the completedseal therein as itwould appear if viewed from the side and top, respectively;

Fig. 2 is an enlarged cross-sectional view taken along the line IIII ofFig. 1 in the direction of the arrows, showing the mainribbon conductorhermetically sealed within the stem portion of the completed lamp;

Fig. 3 is an enlarged cross-sectional view of the stem portion of thelamp envelope taken along the line III'IIl of Fig. 1, in the directionof the arrows, showingthe electrode with its metal foil Wrappinghermetically sealed within the stem of the; completed lamp;

Fig. 4 is a perspective view of the ribbon leading-in conductor andelectrode supporting assembly just prior tofits insertion into the stemtube portion of the lamp envelope; v

Fig.1 5 is an exploded side view of the ribbon portion of the assemblyshowing the various. components and their relation to each other priorto their jointure to form one electrical unit;

Fig. 6 is a fragmentary cross-sectional view of a short are lamp atonestage of its fabrication showing the.

alongthe line VII-VII of Fig. 6, in thedirection' of' the arrows,"showing the relationship between the ribbon applicable to themanufacture of other types of high.

pressure-gaseous discharge lamps, the invention isusually employed inconjunction with the manufacture of short arc mercury discharge lampsand hence has-been so illus- H ribbon conductor and electrode supportingassembly of this-invention. As iswell known, short are lamps in generalconsist of an envelope of vitreous lighttransmitting materialhaving ahigh" melting point, such as quartz, and having a substantiallyspherical bulb portion a 12 and two oppositely disposed arms or stemtube portions 14of substantially equal length extending outwardlytherefrom. Sealed within each of the stem tube portions 14 is a mainribbon conductor 26 one end of which is electrically connected to anelongated electrode 19 and the-other end of which is connected to a pairof terminal strips 32. A portion of each of the electrodes 19 is sealedin the stem portion 14 so'that the electrodes 19 are positioned in apredetermined spaced relation within the spherical bulb portion 12,which encloses a' suitable ionizable. medium such as mercury vapor orxenon gas. The electrodesl9 are preferably fabricatedfrom tungsten andmay have tungsten coils 18 afiixed to their inner end portions whichcoils 18 may contain a small amount of efficient-electron emittingmaterial, such as thorium, to facilitate starting of thearc discharge,as is well known in the art. The essence of this invention resides inthe fabricationof the ribbon leading-in conductor and electrodesupporting assembly and the manner in which it is positioned and sealed.within the stern portion 14 of. the lamp envelope. and these arehereinafter more fully described.

.As illustrated in the exploded view of the ribbon portion of theassembly shown in Fig. 5, a main ribbon conductor 2.6 of thin refractorymaterial, such as molybdenum ribbon approximately 5.5 mm. wide and.0012" thick, is interposed between two relatively long terminal strips32 of a suitable refractory metal which serve as external electricalconnectors for the lamp 10. In order to facilitateconnection with asource of electrical power it has been found desirable to fabricate theterminal strips 32 from moly ribbon having a substantially greaterthickness than the main ribbon conductor 26, as for example .00 Toinsure a strong electrical junction between the ribbon conductor 26: andterminal strips 32 during thelife of the lamp 10. it has been foundadvantageous toplace thin narrow. strips 44 of. a suitable metal foil(see Fig. 5), such as'nickel or platinum of approximately .0Ol,'.'-thickness, between the conductor 26 and each of the strips 32 to serveas a brazing agent. A more perfect bond between the quartz and edges ofthe main ribbon conductor 26 may be obtained and the overall qualityand..-strength of the finishedseal improved by fabricating the ribbonconductor 26 from a molybdenum ribbon M4" wide. and approximately..0016thickwhich ribbon is subsequently chemically etched until its maximumthickness is no greater than approximately .0012" and its outer edge tiare gradually reduced to extremely thin sections to form a wellknownfeather edge. Although the current carrying capacity of a ribbon ofthese di.- mensions is limited to approximately. l0 amperes, increasedcurrent carrying capacity, as for example up to approximately 30amperes, may be obtained by appropriately increasing the ribbondimensions and forcecooling the, exposed portions of the moly terminalstrips 32 to prevent the deleterious effect of oxidation which wouldyup-at the-highambient temperature conditions generated by a lamp ofsuch wattage.

-- Superimposed over each of the terminal strips 32 and overlapping theend of the ribben conductor 26 are two retaining tabs 30 which may befabricated from relatively short sections of resilient metal ribbon,such as molybdenum .004" thick. The end portions of the retaining tabs30 which extend beyond the edge of the ribbon conductor 26 are bent atright angles to the plane containing the ribbon conductor 26 to form apair of oppositely disposed end panels. In order to prevent cracks fromoccurring in the region of the juncture of the retaining tabs 30 andterminal strips 32 with the relatively thin main ribbon conductor 26 asa result of the ledge or sharp edges left exposed, a pair of protectivestrips or flaps 28 of refractory material, such as molybdenum .0006" inthickness, are provided and positioned so as to overlap the aforesaidconnected members and form a sheath over the juncture formedtherebetween. .The protective flaps 28 also insure a good electricalconnection between the members by obviating a high resistance juncturewhich could cause the ribbon to burn through and lead to subsequentlampj failure and serve to shield the electrical connection between themain ribbon conductor 26 and terminal strips 32 from any strains whichmay arise as a result of the unequal expansion and contraction of thequartz and metal portions of the seal during the normal operation of thelamp 10.

The other end of the main ribbon conductor 26 is interposed between theends of a pair of connector strips 22 of refractory metal,'such asmolybdenum, which serves to connect the ribbon conductor 26-to theelectrode 19. To facilitate electrical connection with the electrode 19the connector strips 22 may be of substantially greater thickness thanthe ribbon conductor 26, as for example .004". A firm bond between saidconduct0r26 and strips 22 may be obtained by inserting therebetween .twostrips 44 of suitable metal foil to act as a brazing agent (see Fig.5).- A pair of protective flaps 24 may be provided to' present asubstantially smooth curved sealing surface overthe ledge formed by thejuncture of the relatively thin ribbon conductor 26 with the connectorstrips 22 and to protect the electrical connection therebetween fromexcess strains during the heating and cooling of the completed seal.After the main ribbon conductor 26, terminal strips 32,-retaining tabs30, connector strips 22, metal foil strips 44, and protective flaps 24and 28 have been assembled as heretofore described, they areelectrically joined together, such as by welding, to form the ribbonconductor member of the leading-in conductor and electrode supportingassembly which member is then ready for connection with theother-partsof the assembly as hereinafter described. 1 I

An elongated electrode 19 having a coil 18 of refractory 1 metalattached to its inner end portion is inserted into thereof up tothe coil18 may be encased in a wrapping of refractory metal foil 16, such asmolybdenum ribbon .0006 thick, to prevent cracks from occurring in thecompleted seal when the electrode 19 becomes heated and expands duringthe operation of the lamp 10. The

. free end portions of the connector strips 22 which extend beyond theend of the main conductor 26 are bent outwardly to form a V-shapedpocket into which the foil encased electrode tip 20 is inserted andelectrically connected. .The terminal strips 32 are connected to apositioning tab. 42 by a rod 38 of refractory metal suchas molybdenum.For addedstrength the positioning tab 42 may consist of a pair of metalribbons of unequal length welded together and affixed to each side ofthe rod 38. A pair of positioning clips 40, such as of arcuateretrovert'edmolybdenum strips for example, are attached to oppositesides of an intermediate portion of the rod 38 to .serve as compressible members to insure accurate positioning of the electrode andribbon conductor assembly within the stem tube14. A pair ofplano-cylindrical quartz rods 36 are formed by bisecting a quartzcylinder of the same diameter as the aforementioned quartz tube 34,'asfor example A"; The rods 36 are inserted between the edges of theretaining tabs 30 and the quartz tubing 34'with their plane surfacesfacing inwardly and are resiliently 'held in this position so that themain ribbon conductor 26 and its lapping end connections together withthe'electrode tip 20 are totally enclosed to form a compositelaminous'core member of substantially cylindrical configuration havingone end of the electrode 19 and the terminal strips 32' and theassociated electrode positioning elements attached thereto protrudingfrom opposite ends thereof.

The cylindrical core member formed as hereinbefore described is theninserted into the tubular stem portion 1 4 of "the lamp envelope, asshown in Fig. 4. The core member and electrode supporting assembly areinserted into the tubular stem portion 14 until the positioning clips 40'are forced into intimate contact with the inner surfaces of'the tubularportion 14 and upon further penetration are c'ompressed inwardly tofrictionally engage the inner surfaces of the tube 14. This enables theassembly to be'a'ccurately positioned'within the stem tube portion 14 sothat the electrodes 19 can be oriented in the desired preselectedposition within the spherical bulb portion 12. After the electrodes 19are properly positioned, the positioning tab'42 is sealed in the tubeportion 14 to anchor the inserted core member and associated elements intheir respective positions and to seal off the envelope for evacuationby heating the end of the stem tube portion 14 to plasticity and formingan air tight seal 45 around the tab 42, as shown in Fig. 6. At thisstage of the fabrication of the seal the main ribbon conductor 26 isinterposed between the plane surfaces of the rods 36 ofsemi-hemispherical cross-section which rods 36 are, in turn, {completelyenclosed by the walls of the tubular stern portion 14, as shown in Fig.7.

-The spherical bulb portion 12 and tubular stem portions 14 of the lampenvelope are now evacuated through an exhausttubulation 15 having aconstriction 13 formed th'erein'adjacent to the spherical bulb portion12. After the envelope has been evacuated to the desired pressure, asfor example .001 mm. of mercury, the exhaust tubulation' 15 is sealedoff at a point beyond the constriction 13 by suitable sealing fires (notshown). The outer end portion of the stem tube 14 is then held androtated, as in a rotatable chuck for example (not shown), while a hightemperature flame (also not shown) is directed to the region of thestern portion 14 adjacent to the outermost edge of the semi-cylindricalrods 36, as viewed in Fig. 6 until the quartz becomes plastic and thewall portion of thefstern 14 thereat is forced inwardly by atmosphericpressure and fuses with the rods 36 to form' a solid mass. The tubularstem portion 14 is constantly rotated and the high temperature sealingfires progressively advanced inwardly toward the spherical bulb portion12, as viewed in Fig. 6, until the neck portion of the envelope betweenthe tube portion 14 and spherical portion 12 is reached. The

main ribbon conductor 26 and outer end portion of the electrode 19 arethus sealed'in a solid cylinder of fused quartz,as shown in Figs. 2 and3, Due to the vacuum within'the envelope the quartz tube 34,semi-cylindrical rods 36, and'the walls of the stem tube 14 are drawninto' intimate contact with the metal portions of the core memberwhenthe quartz is in a plastic state. This permits a uniform high strengthseal to be formed and the use of the quartz tube 34 and semi-cylindricalrods 36 as core members prevenfthe main conductor 26 from beingdeleteriously deformed or damaged during the sealing operation.

After the seal has been completed as hereinbefore described, the tip(not shown); previously formed on the exhaust tube 15 is broken and theenvelope filled with a predetermined amount of mercury or suitableionizable gas, such as xenon, and the exhausttube 15 tipped-off bysuitable fires at the constriction 13 to form a seal tip 11. The outerend portion of the stem 14 beyond the region of the seal is then cut offby a wet cutting wheel 46, as shown in Fig. 6, care being exercised toprevent cutting of theterminal strips 32. After'the cutting operationhas been completed 'the terminal strips 32 are severed at a pointadjacent to the end of the rod 38 thereby com pleting the fabrication ofthe'larnp.

It will be recognized from the foregoing that a simple but mosteffective means of protecting a ribbon conductor andits edges fromdeformation and damage during the sealing operation necessary to embedit within the stem tube portion of a gaseous discharge lamp has beenprovided. Moreover, this is accomplished by providing a quartz tube anda pair' of semi-cylindrical rods resiliently held in an abuttingrelation tototally enclose the main ribbon portion and end portion ofthe electrode and form a cylindrical core member to protect the ribbonassembly and maintain the electrode in the proper position duringsealing.

Although a preferred embodiment of the invention has been illustrated,itwill'be understood that other modifications may be made withoutdeparting from the spirit and scope of the appended claims.

We claim:

1. A gaseous discharge lamp comprising an envelope having a bulb.portionand outwardly extending fused sternportions, an ionizable mediumenclosed within said envelope, and ribbon leading-in conductor andelectrode assemblies sealed through each of said stern portions, each ofsaid assemblies comprising a main ribbon conductor of thin refractorymaterial-having its outer end portion interposed between and fastened toa plurality of paired metallic strips arranged in overlapping relationtherewith, at least one pair of said strips extending longitudinally ofsaid main conductor to serve as external connectors and another pair ofsaid strips adapted to serve'as retaining members, an elongatedelectrode having an end adapted for connectionwith said main conductor,a wrapping of metal foil'around said electrode end, and asecondpluralityof paired and overlapping metal strips'joining the said foil enwrappedend of said electrode with the end of said main conductor opposite thefirst said plurality of strips, said assemblies being centrally embeddedandhermetically sealed within said fused stem portions andlongitudinally positioned therein so that the end sections of the saidlongitudinally-extending strips protrude fromthe stems-and the free endsof the electrodes project into the bulb portion of the envelope inpredetermined spaced apart relation.

2. A short arc gaseous discharge lamp comprising a light-transmittingenvelope having a spherical bulb portion with two oppositely disposedarms extending outwardly therefrom,'an' ionizable medium enclosed withinsaidenvelope, and ribbon leading-in conductor and electrode assembliessealed through each of said arms, each of said assemblies comprising amain ribbon conductor having its outer end portioninterposed between andfastened to three pairs of refractory metal strips arranged in smoothsealing surface, an elongated electrode having one end shaped to form aflat wedge-shaped tip, a wrapping of metal foil around said flattenedend portion and 'adjacent body portion of said'electrode, anda secondgroup of paired refractory metal strips comprising an inner pair ofstrips of substantially greater thickness than said main conductorattached to the end of said main conductor opposite the first said groupof strips and connected to the said foil enwrapped end of the electrdoein enveloping relation therewith, and an outer pair of stripsproportioned and disposed to cover the juncture between the mainconductor and said inner pair of strips, said main ribbonconductonhaving extremely thin tapered edges and said assemblies beingcentrally embedded and hermetically sealed within each of said arms andof sufficient length that the end sections of the saidlongitudinally-extending strips protrude from the arms and the free endsof the electrodes project into the spherical bulb portion of theenvelope in opposite and predetermined spaced apart relation. I

3. An electrically-conductive ribbon type seal for a gaseous dischargelamp having an envelope with a bulb portion and a fused tubular stemportion comprising a main leading-in conductor of refractory metalribbon having extremely thin tapered edges, an elongated electrodehaving a flattened end portion adapted for connection with said mainconductor, a wrapping of metal foil around said flattened end portionand adjacent body portion of said electrode, a pair of metal connectorstrips fastened to one end of said main conductor and the flattenedfoilenwrapped end of said electrode, said main conductor and electrodeends being interposed between said connector strips in overlappingrelation therewith, the other end of said main conductor beinginterposed between and connected to a plurality of paired metal stripsarranged in overlapping relation, at least one pair of said stripsextending longitudinally of said main conductor to serve as externalconnectors and another pair of said strips being adapted to serve asretaining members, and thin metal flaps covering the junctures betweensaid strips and main conductor to provide a smooth sealing surface, saidconnector and longitudinally-extending strips being substantiallygreater in thickness than said main conductor, and said conjoined mainribbon conductor, strips and foil enwrapped portion of said electrodebeing centrally embedded and hermetically sealed within said fused sternportion and of suflicient length that the said longitudinallyextendingstrips protrude from the end of said stem portion and the free end ofthe electrode projects into the bulb portion of the envelope inpredetermined spaced apart relation with the walls thereof.

4. A ribbon leading-in conductor and electrode assembly for sealing intothe tubular stem portion of a gaseous discharge lamp comprising a mainribbon conductor of refractory metal, an elongated electrode having afiattened end portion and an enlarged opposite end portion, a wrappingof metal foil around the flattened end portion and intermediate bodyportion of said electrode adjoining said enlarged end portion, a sectionof vitreous tubing carried by the foil-enwrapped intermediate portion ofsaid electrode, said tubing being seated against the enlarged portion ofsaid electrode and of such length that the flattened end portion of theelectrode protrudes therefrom, means connecting one end of said mainribbon conductor with the said protruding electrode end portion, theother end of said main conductor being interposed between and connectedto a plurality of metal strips adapted to provide a longitudinallyextending terminal and a pairof oppositely disposed retaining members, apair of matching lano-cylindrical vitreous rods longitudinally insertedbetween said retaining members and the edge surfaces of said tubing,said rods being positioned so that their plane surfaces face inwardlytoward each other, to totally enclose and protect said main rib- 8 r bonconductor and form a'composite laminous core mem ber of substantiallycylindrical configuration adapted to be received by said tubular stemportion.

5. A ribbon leading-in conductor and electrode supporting assembly forsealing into the tubular quartz arm of a short are lamp comprising amain ribbon conductor of molybdenum having extremely thin tapered edges,an elongated electrode having a flattened end portion and a coil mountedat its opposite end portion, a wrapping of metal foil around theflattened end portion and intermediate body portion of said electrodeadjoining said coil, 2. section of heavy-Wall quartz tubing surroundingoppositely disposed and transversely projecting resilient end panels, apair of matching plano-cylindrical quartz rods longitudinally insertedbetween said end panels and the edge surfaces of said tubing, said rodshaving substantially the same outer curvature as said tubing and beingpositioned so that their plane surfaces face inwardly toward each otherto totally enclose and protect said main ribbon conductor and form acomposite laminous core member of substantially uniform cylindricalconfiguration adapted to be received by the tubular arm of said lamp,and means attached to said terminal strips for longitudinallypositioning said core member within said arm including compressiblemembers operable to frictionally engage the inner wall surfaces of saidarm and maintain said member in its assembled position during thesealing-in operation.

6. The method of fabricating and sealing a ribbon leading-in conductorand electrode assembly within the tubular stem portion of a gaseousdischarge lamp envelope comprising, providing an elongated electrodehaving an enlarged body portion and a flattened end portion,wrapping-said flattened end portion and adjacent part of said electrodeadjoining the said enlarged body portion in metal foil, inserting thefoil-enwrapped portion of the electrode into a section of vitreoustubing of such length that the flattened end portion of the electrodeprotudes therefrom when said tubing is seated against the said enlargedbody portion, seating said tubing against said enlarged body portion,connecting the protruding flattened end portion of said electrode with arefractory metal ribbon, aflixing a plurality of metal strips to the endof said ribbon opposite said electrode to provide a longitudinallyextending terminal connector and a pair of oppositely disposedtransverse members, placing a pair of matching plano-cylindricalvitreous rodsbetween said transverse members and the edge surfaces ofsaid tubing to enclose said metal ribbon and adjoining portions of saidelectrode and metal strips and thus form a composite laminous coremember of substantially uniform cylindrical configuration, attaching anelongated positioning member having intermediate compressible extensionsto the free end portion of said terminal connector, inserting saidelectrode and conjoined core member into the tubular stem portion untilsaid extensions frictionally engage the inner wall surfaces of saidstern, orienting said core member and electrode in predeterminedlongitudinal relation with said stem portionby means of said positioningmember, sealing the end of said stem portion over said positioningmember,

evacuating said .envelope and progressively heating the section of saidstem occupied by said core member until the tube walls collapse and fusewith the vitreous tubing and rod portions of said core member tohermetically seal the refractory metal ribbon and foil enwrapped sectionof the electrode in said stem portion, and thereafter separatelysevering said stern and terminal connector at difierent points remotefrom the fused outer end portion of said stem.

References Cited in the file of this patent UNITED STATES PATENTSKettlewell Mar. 30, 1948 Wiener Dec. 29, 1953 Freeman Feb. 23, 1954Unglert Apr. 13, 1954 Hodge Mar. 29, 1955

